The gas-phase thermal reactions of 1-methylbicyclo[3.2.0]hept-2-en-7-one

Abstract

The kinetics of the thermal reactions of 1-methylbicyclo[3.2.0]hept-2-en-7-one have been studied in the gas phase over the temperature range 489–565 K. The primary reaction appears to occur via two parallel first-order homogeneous isomerizations to yield 5-methylbicyclo[2.2.1]hept-5-en-2-one and 2-methylhepta-1,3,6-trien-1-one. Under the experimental conditions employed, 2-methylhepta-1,3,6-trien-1-one undergoes rapid secondary reactions which have heterogeneous components. First-order rate constants for the disappearance of reactant, obtained by an internal standard technique, fit the Arrhenius relationship log k/s^–1= 14·50 ± 0·28 –(183·8 ± 2·8 kJ mol^–1)/2·303RT. The mode of reaction and Arrhenius parameters are different from those found for compounds with the bicyclo[3.2.0]hept-2-en-6-one structure and can be rationalized by a diradical mechanism.